By the time you consider using a bottle, a Skippy container is just not going to cut it! It needs to be at lease 0.5L, but more like a liter plus, a 'Nalgene-like' bottle works best, I have a MadRock 'Bigmouth' which is perfect!!
But lets face it, this sort of measure only needs to be taken in very bad conditions, not when it's raining...

humph - be like a real WOMAN! Tiptoe drunk in someone elses oversized sandals past the 30 foot drop and the sleeping comrade at the edge of the cave entrance into the dark and the rain to hover over the edge of one of em steep berg slopes. And yes, we go in groups out there too.